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This commit adds four litmus tests showing that a failing cmpxchg() operation is unordered unless followed by an smp_mb__after_atomic() operation. Suggested-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Cc: Alan Stern <stern@rowland.harvard.edu> Cc: Will Deacon <will@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: David Howells <dhowells@redhat.com> Cc: Jade Alglave <j.alglave@ucl.ac.uk> Cc: Luc Maranget <luc.maranget@inria.fr> Cc: "Paul E. McKenney" <paulmck@kernel.org> Cc: Akira Yokosawa <akiyks@gmail.com> Cc: Daniel Lustig <dlustig@nvidia.com> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: <linux-arch@vger.kernel.org> Cc: <linux-doc@vger.kernel.org> Acked-by: Andrea Parri <parri.andrea@gmail.com>
35 lines
499 B
Plaintext
35 lines
499 B
Plaintext
C cmpxchg-fail-ordered-1
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(*
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* Result: Never
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*
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* Demonstrate that a failing cmpxchg() operation will act as a full
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* barrier when followed by smp_mb__after_atomic().
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*)
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{}
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P0(int *x, int *y, int *z)
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{
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int r0;
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int r1;
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WRITE_ONCE(*x, 1);
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r1 = cmpxchg(z, 1, 0);
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smp_mb__after_atomic();
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r0 = READ_ONCE(*y);
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}
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P1(int *x, int *y, int *z)
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{
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int r0;
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WRITE_ONCE(*y, 1);
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r1 = cmpxchg(z, 1, 0);
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smp_mb__after_atomic();
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r0 = READ_ONCE(*x);
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}
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locations[0:r1;1:r1]
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exists (0:r0=0 /\ 1:r0=0)
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